1. Field of the Invention
This invention relates to cutting instruments and particularly to knives that are used for performing surgical procedures.
2. Background Discussion
Recently, several micro-surgical procedures have been developed that call for the surgeon to make incisions to very closely controlled depths. An example of such surgery is the radial keratotomy techniques presently being developed to reduce or eliminate myopia. These procedures require that a plurality of incisions be made in the cornea of the eye, commonly to a depth on the order of 0.5 mm to 0.6 mm. If these incisions are made too deep, serious damage to the eye can result.
3. Description of Known Prior Developments
Several systems have been proposed for mechanically controlling the depth of the surgeon's incision. U.S. Pat. No. 2,932,296 to Sanders shows a blade receiving appliance that is primarily used for guiding the direction of large incisions and that, incidentally, functions as a control of the cutting depth. Such apparatus may be useful in general surgery but is not believed to be useful in the majority of microsurgical techniques that are performed under a microscope and on a generally small-sized surgical field. Also, the surgeon desires to keep the cutting edge in constant view while the cutting is performed so that maximum control can be exercised. The structure proposed in the above-noted patent would tend to make such observation of the cutting edge difficult.
Another solution proposed is to use a stop element that is frictionally mounted on the blade prior to the procedure, as shown in U.S. Pat. No. 3,945,117 to Beaver. This system requires the use of a separate, sterilely maintained gauge element for setting the stop at the proper position. With this type of depth control, resetting the stop during a procedure can be time-consuming and awkward.
Another method of controlling blade depth involves the use of a blade gauge that is used in conjunction with a blade holder and separable cutting blades that are freely positioned in the holder. In such an approach, the holder is moved along a flat surface and the distance from the tip of the holder to the tip of the blade is noted from a graduated measuring line. However, the guide merely functions to indicate proper cutting depth and does not include means for varying the position of the blade. Further, there is a risk of damaging the cutting edge by contact with the gauge as the exposure is being measured.
Depth control of cutting blades has been accomplished in fields other than surgery. A knife having a cutting depth control feature is shown in U.S. Pat. No. 1,843,535 to Arnold. However, the arrangement shown in this patent does not provide for fine adjustment of the position of the stop element and requires the use of additional tools for resetting and locking the stop element in a desired position. It is believed that these factors would limit the acceptability of this design for surgical use.